(1) Field of the Invention
This invention relates generally to digital cameras and relates more specifically to camera shutters driven by a linear motor.
(2) Description of the Prior Art
In photography, a shutter is a device that allows light to pass for a determined period of time, for the purpose of exposing photographic film or a light-sensitive electronic sensor to light to capture a permanent image of a scene.
As light travels through a lens opening (aperture), the shutter opens and closes in a timed fashion to determine how long the image sensor (“film”) gets exposed to a scene. The exposure time has a most important impact upon the quality of an image. Conventional film cameras are using usually mechanical shutters while digital cameras are often using digital shutters. It is a challenge for the designers of digital cameras to design a shutter mechanism for digital cameras that can be exactly controlled.
The aperture of an optical system is the opening that determines the cone angle of a bundle of light rays that come to a focus in the image plane. The aperture determines how collimated the admitted rays are, which is of great importance for the appearance at the image plane. A narrow aperture will result in sharpness at the image plane, while a wide aperture will result in sharpness for light rays with the right focal length only. This means that a wide aperture results in an image that is sharp around what the lens is focusing on and blurred otherwise. The aperture also determines how many of the incoming rays are actually admitted and thus how much light that reaches the image plane, i.e. the narrower the aperture, the darker the image.
In addition, with the advancement of small portable terminals equipped with cameras having zoom functions and shutters there is a requirement of compact size shutters. Therefore there is a need of precise, compact size shutters, which are easily to be assembled.
Solutions dealing with camera shutters are described in the following patents or patent publications:
(U.S. Pat. No. 6,733,192 to Watanabe) teaches an electromagnetic actuator having a rotor magnetized to have a plurality of poles; a base rotatably supporting the rotor; a yoke having a plurality of magnetic pole portions that are formed so as to face an outer peripheral surface of the rotor and that generate different magnetic poles; a magnetizing coil; and a bobbin/presser member which is disposed on an outer periphery of the yoke, around which the coil is wound, and with which a pressing portion for pressing the yoke against the base and for supporting the rotor is formed integrally. A camera blade driving device according to the present invention has a base having an exposure opening; a shutter blade or a diaphragm blade that is rotatably supported by the base; and an electromagnetic actuator including a rotor that is magnetized to have a plurality of poles and that is rotatably supported by the base, a yoke having a plurality of magnetic pole portions that are formed so as to face an outer peripheral surface of the rotor and that generate different magnetic poles, a magnetizing coil, and a bobbin/presser member which is disposed on an outer periphery of the yoke, around which the coil is wound, and with which a pressing portion for pressing the yoke against the base and for supporting the rotor is formed integrally, the electromagnetic actuator driving the shutter blade or the diaphragm blade. Accordingly, the parts count is reduced, and the assembly task is simplified, while cost is lowered.
(U.S. Pat. No. 7,350,990 to Shin et al.) discloses a shutter device for use with a camera lens assembly, wherein the shutter device includes a shutter base, a shutter blade which is rotatably mounted on the shutter base, a magnet movably coupled to the shutter base so as to enable rotation of the shutter blade, and a yoke extending lengthwise while facing the magnet wherein the movement range of the shutter base is limited within a length of the yoke. The zoom-in/zoom-out operation is enabled by moving only the shutter base, thus enabling a compact size fabrication of the camera lens assembly. The shutter blade is easily installed adjacent to a diaphragm, and the operational speed of the shutter blade is controlled by adjusting the structure of an electronic coil.
U.S. Patent Publication (US 2007/0110433 to Masahiko) describes a shutter driving apparatus for a camera module having a shutter driving section constructed to slidingly move shutter blades provided to a camera lens module in both sideward directions to thereby open and close a lens opening. The shutter driving apparatus comprises a lens housing; a pair of shutter blades provided to the lens housing to be slidingly moved in a lengthwise direction of the lens housing to thereby open and close a lens opening of the camera lens module; and a pair of shutter driving sections respectively connected to the shutter blades via rotation links and each being configured for creating a pair of electromagnetically-opposite electromagnet poles and having a permanent magnet positioned between the poles such that a permanent magnet with at least one of the poles and connected to the rotation link is rotated due to a magnetic field created as current is applied to the electromagnet, to slidingly move an associated shutter blade.